The present invention relates to apparatus and methods for guiding a nuclear fuel bundle into a channel and particularly relates to apparatus and methods for guiding a fuel bundle having a plurality of nuclear fuel rods, water rods and a plurality of spacers into a fuel bundle channel through an open upper end of the channel.
In the fabrication of fuel bundle assemblies for boiling water nuclear reactors, it is customary to lower the fuel bundle channel onto the fuel bundle. The fuel bundle comprises an array of nuclear fuel rods and one or more water rods with spacers at axially spaced positions along the fuel bundle. The channel comprises essentially an elongated rectilinear sleeve which, in assembly with the fuel bundle, engages the outer margins of the spacers. This conventional procedure for lowering the channel about the fuel bundle is practical in part because the channel weighs a small percentage of the overall weight of the fuel bundle, e.g., 50 to 60 pounds, and can be easily guided manually onto the bundle with minimum risk of damage to any of the fuel assembly components.
In certain fuel bundle assemblies, however, mechanical support for the fuel assembly is provided solely by a channel transition assembly and the bundle upper tie plate. The channel transition assembly typically consists of the channel attached at its bottom to a transition nose piece. The nose piece is dimensionally very similar to the dimensions of the outside of a lower tie plate but it does not have the lower grid plate that holds the fuel rod and water rod lower end plugs. Because the nose piece in the channel transition assembly is pre-attached to the channel, the conventional assembly procedure noted above cannot be used and the procedure must be reversed, i.e., the bundle must be lowered down into the channel. This substantially increases the risk of damage to fuel bundle components, especially to the fuel spacers, since the heavier weight of the bundle, e.g., 600 pounds, renders manual control of the position of the bundle more difficult while the fuel bundle is being lowered into the channel. The lowermost spacers of the fuel bundle are especially susceptible to damage during this procedure if the bundle and channel are misaligned relative to one another by as little as a tenth of an inch.